The lack of the strat map editor is a major pain (doing things manually is much more complex, time consuming, and buggy. And doesn't look as good either), but it's not a hard limit. Not being able to add new factions hurts a lot. As does the CTD when you click on the faction info button if you've created a new campaign.

The frustrating thing is that some of the modding issues we have (e.g. adding new factions) are the same that we had back in MTW, but were then resolved with VI. So we've actually gone backwards in some respects in terms of modability from where we were.